This invention relates to a method of environmental control.
In particular, but not exclusively, this invention relates to a method of environmental control for plant material grown on solid medium. Reference throughout the specification will be made to the plant material as being somatic embryos, although it should be appreciated that the present invention can be applied to other plant material.
The growing of somatic embryos on a solid medium is still a relatively new science. Typically, the solid medium is a gelatinous/solid mixture with various ingredients such as minerals, sugars and amino acids which are required by the growing embryos. The medium in its liquid form is usually poured into containers such as Petri dishes. Once the medium has solidified, the embryos are placed onto the medium and the dish is covered with a plastic or glass lid or closure. The margins where the closure and dish overlap is sealed with a clear cling film. Cling film is used as it provides a seal against possible microbial infection which could be fatal to the embryos.
Cling film of the sort presently used is gas and vapor impermeable. While such cling film can effectively seal dishes against microbial infection, there are other problems associated with the use of this film.
One problem is that the use of vapour and gas impervious enclosure may result in build-up of condensation on the underside of the closure. This condensation not only causes viewing problems but it also causes more significant physiological problems: namely, condensate (generally water) may form which can drop back onto the medium. The medium has certain properties including a defined concentration of solutes which govern the rate at which water can be taken up by the growing embryos. It is important that the concentration of the various ingredients of the medium are at an optimum value for successful embryogenic development. Free water dropping onto the medium from the film can therefore cause the effective concentration of essential ingredients as received by the embryos to alter and can adversely affect the growth of the embryos.
There are believed to be additional problems to those described above caused by the use of traditional cling film.
While is was known in the past that fully developed plants have a gaseous exchange with the atmosphere, it was thought that this did not apply to plant embryos which were considered to be totally dependent on their internal environment. The basis of this belief was the understanding that embryos do not have a requirement for fixing carbon dioxide, as embryos do not photosynthesise unlike fully developed plants.
It is now believed by the applicant that embryos do have a gaseous exchange with the atmosphere. In the case of embryos grown under typical closure, there are strong indications that under the closure there is a build-up of ethylene and a possible depletion of carbon dioxide and oxygen. Ethylene is a bioactive substance and is thought to cause elongation of the cells in he embryos, perhaps to such an extent that the cells revert to non-embryogenic types. Auxins cause a similar undesirable effect on embryogenic tissues. The effect of the changing concentrations of oxygen and carbon dioxide is also thought to be harmful to the tissue.
It is an object of the present invention to address the above problems, or at least to provide the public with a useful choice.
Further objects and advantages of the present invention will become apparent from the following description which is given by way of example only.